Method of manufacturing a carbon material and the carbon material

ABSTRACT

A method of manufacturing a surface-modified carbon material is provided that can form a layer of a metal or the like on the surface in a simple manner and with adhesion performance. The surface-modified carbon material is also provided. The method is characterized by heat-treating a carbon substrate together with a carbon member other than the carbon substrate, the carbon substrate embedded in a surface modifying agent comprising a pyrolytic hydrogen halide generating agent and metal particles containing a transition metal. More specifically, a carbon substrate ( 2 ) is embedded in powder ( 3 ) containing a pyrolytic hydrogen halide generating agent such as ammonium chloride and metal particles containing a transition metal such as stainless steel, and the carbon substrate ( 2 ) is heat-treated together with a carbon member other than the carbon substrate, such as a the graphite crucible ( 6 ).

TECHNICAL FIELD

The present invention relates to a method of manufacturing asurface-modified carbon material, and to the surface-modified carbonmaterial.

BACKGROUND ART

A carbon material is light in weight and excellent in chemical andthermal stability and has good thermal conductivity and electricalconductivity even though it is a non-metal material. A carbon materialis light in weight and excellent in chemical and thermal stability andhas good thermal conductivity and electrical conductivity even though itis a non-metal material. However, when a layer of a material other thancarbon is formed on the carbon material, there is a problem in adhesionperformance between the carbon material and the layer of the othermaterial.

As a method for improving the adhesion performance, Patent Documents 1and 2, for example, describes that, by treating a carbon substrate withhalogenated chromium gas, a chromium carbide layer comprising Cr₂₃C₆ isformed on the surface, and the chromium carbide layer is coated with ametal by thermal spraying. However, this technique has the followingproblems. It takes a very long time to form a layer comprising Cr₂₃C₆that can withstand the thermal spraying of a metal. Also, the treatmentis complicated and troublesome; for example, it is essential to carryout the treatment in a hydrogen gas atmosphere and the treatment needsto be performed under a reduced pressure.

CITATION LIST Patent Literature

-   [Patent Document 1] Japanese Unexamined Patent Publication No.    8-143384-   [Patent Document 2] Japanese Unexamined Patent Publication No.    8-143385

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The present invention has been accomplished in view of the foregoingproblems, and it is an object of the present invention to provide amethod of manufacturing a surface-modified carbon material that can forma layer of a metal or the like on the surface with good adhesionperformance in a simple manner, and to provide the surface-modifiedcarbon material.

Means for Solving the Problems

The present invention provides a method of manufacturing a carbonmaterial, characterized by heat-treating a carbon substrate togetherwith a carbon member other than the carbon substrate, the carbonsubstrate embedded in a surface modifying agent containing a pyrolytichydrogen halide generating agent and metal particles comprising atransition metal.

Examples of the carbon member include a container made of carbon, suchas a graphite crucible, and carbon powder. The heat-treating may beperformed under normal pressure. Moreover, the metal particlescomprising a transition metal may be transition metal particles or alloyparticles containing a transition metal, and it is particularlypreferable to use an alloy containing Cr, such as stainless steel. Thereason is that, by using the alloy containing Cr, a metal carbidecontaining Cr and a metal carbide layer can be formed by the heattreatment at one time.

The present invention also provides a carbon material characterized byhaving a metal carbide layer containing M₂C or M₃C₂ (M: transition metalelement) on a carbon substrate, and having a metal layer or an alloylayer on the metal carbide layer. It is preferable that the M be Cr. Itis also preferable that the metal contained in the metal carbide layerbe a transition metal, such as Cr, Fe, and Ni. It is preferable that themetal carbide layer have a thickness of 100 μm or less.

This carbon material can be manufactured desirably by the carbonmaterial manufacturing method of the present invention. By usingstainless steel powder as the metal powder containing a transition metalin the manufacturing method, a metal carbide layer containing Cr₂C orCr₃C₂ and containing Ni and Fe can be easily formed on the carbonsubstrate at one time.

Advantages of the Invention

The carbon material manufacturing method of the present invention makesit possible to shorten the treatment time and at the same time toeliminate the need of supplying a hydrogen gas by using a carbon membersuch as carbon powder and a container made of a carbon material.Thereby, the surface modification of the carbon substrate can be mademore easily. This makes it possible to improve the adhesion performanceof the carbon substrate with a layer of a metal or the like that is tobe later formed on the surface, and also to improve the strength of theresulting carbon material over the carbon substrate.

Moreover, pressure reduction is not needed, and the heat-treating can beconducted under normal pressure (in an atmospheric pressure). Thus, thetreatment can be conducted in a simple manner.

The carbon material according to the present invention shows goodadhesion performance with a layer of metal or the like that is to beformed later, and also has improved strength.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a view illustrating one example of a heating apparatus usedfor a method, according to the present invention, of manufacturing acarbon material.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the present invention will be described in detail.

In the present invention, the method of manufacturing a carbon materialincludes heat-treating a carbon substrate together with a carbon memberother than the carbon substrate, the carbon substrate embedded in asurface modifying agent (in a powdery state) comprising a pyrolytichydrogen halide generating agent and metal particles containing atransition metal.

According to the present invention, the method of manufacturing a carbonmaterial makes it possible to form a metal carbide layer on the surfaceof the carbon substrate in a simple and easy manner, and the methodallows the carbon material to have good adhesion performance with alayer of a metal or the like that is later formed on the carbonmaterial. Examples of the method of later forming a metal layer or thelike on the carbon material include plating and thermal spraying, and anexample of the method that achieves particularly good adhesionperformance is plating.

In the carbon material manufacturing method of the present invention,the carbon substrate to be treated is heat-treated together with acarbon member other than the carbon substrate. Examples of the carbonmember include a container made of carbon, such as a graphite crucible,and carbon powder. By heat-treating the carbon substrate to be treatedtogether with the carbon member in this way, a metal carbide layer canbe formed on the carbon substrate in a short time. The reason isbelieved to be that by using the carbon member, the materials containedin the powder, such as the transition metal and the pyrolytic hydrogenhalide generating agent, can be utilized efficiently for the surfacetreatment of the carbon substrate, so the necessary heat amount can bereduced.

With a treatment time of less than 1 hour, the metal carbide layer canbe formed without color unevenness and substantially uniformly on thecarbon substrate. This metal carbide layer can be formed sufficientlyeven with a treatment time of as long as 30 minutes. The treatment timemay be longer, for example, 1 hour or longer, if the metal carbide layerneeds to be thicker.

It is preferable that the heat treatment be performed at from 800° C. to1200° C. By performing the treatment within this temperature range, thecarbon substrate can be treated efficiently. If the temperature is toolow, it is possible that the formation of the metal carbide layer may beslow. If the temperature is too high, it is possible that the powderthat has not reacted in the heat treatment may be thermally melted andbonded to the carbon substrate.

It is preferable that the heat-treating be performed under normalpressure. Since the treatment can be performed under normal pressure,the equipment such as a vacuum pump is unnecessary, and the timerequired for reducing the pressure is also unnecessary. As a result, thetreatment becomes simpler, and the treatment time reduces. Although itis possible to perform the treatment under reduced pressure, it maybecome difficult to cause an efficient reaction of hydrogen halide sincethe pyrolytic hydrogen halide generating agent may undergo violentdecomposition at low temperature, and also, it is possible that thepowder may scatter.

The carbon material manufacturing method of the present invention doesnot require introduction of hydrogen gas. Therefore, safety is improved,and the treatment can be conducted easily. It is, however, possible tointroduce an inert gas such as nitrogen gas, if necessary.

Hereinbelow, the components and members used in the present inventionwill be described.

Examples of the carbon substrate include, but not particularly limitedto, isotropic graphite materials, anisotropic graphite materials, andcarbon fiber materials. It is preferable that the carbon substrate havea bulk density of from 1.4 g/cm³ to 2.1 g/cm³, an average pore radius of10 μm or less, and a porosity of 40% or less.

The pyrolytic hydrogen halide generating agent is such that is kept in asolid state under room temperature and normal pressure but is decomposedby heating to generate a hydrogen halide such as hydrogen chloride,hydrogen fluoride, and hydrogen bromide. It is preferable that the heatdecomposition temperature of the pyrolytic hydrogen halide generatingagent be 200° C. or higher, so that the handling before the heating canbe easy. The hydrogen halide generated from the pyrolytic hydrogenhalide generating agent reacts with the transition metal during the heattreatment and produces a metal halide gas. By treating the carbonsubstrate with the metal halide gas, the metal carbide layer can beformed on the surface of the carbon substrate. Since the treatment ofthe carbon substrate is conducted with gas as described above, the metalcarbide layer can be formed substantially uniformly on the carbonsubstrate even when the carbon substrate has a complicated shape with,for example, holes and grooves.

It is preferable that the pyrolytic hydrogen halide generating agent beammonium chloride from the viewpoint of availability.

It is sufficient that a transition metal is contained in the metalparticles containing a transition metal. Examples include a mixturepowder of a transition metal and another metal, and an alloy powder of atransition metal and another metal. Examples of the transition metalinclude Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, and Ta, but thetransition metal is not particularly limited as long as it reacts withthe hydrogen halide and produces a metal halide gas. The produced metalhalide gas reacts with the carbon in the surface of the carbon substrateand produces a metal carbide. It is preferable that Cr be contained inthe transition metals from the viewpoint of its high reactivity. It ispreferable that the metal particles be an alloy powder containing Cr,and an example is stainless steel.

Especially when using metal particles comprising stainless steel, whichis an alloy containing Cr, Ni, and Fe, a layer containing Ni, Fe, andchromium carbide is formed at one time of the heat treatment.

It is particularly preferable to use a powder containing stainlesssteel, which is an alloy containing Cr, Ni, and Fe, and ammoniumchloride for the heat treatment, from the viewpoints of handling andcost.

Examples of the carbon member include a container made of carbon, suchas a graphite crucible, and carbon powder.

With the use of the carbon member, the treatment time of the carbonsubstrate can be shortened, and the need of supplying a hydrogen gas canbe eliminated. As a result, the surface modifying of the carbonsubstrate can be achieved in a simpler manner and more easily. Thismakes it possible to improve the adhesion performance of the carbonsubstrate with a layer of a metal or the like that is to be later formedon the surface, and also to improve the strength of the resulting carbonmaterial over the carbon substrate. Moreover, pressure reduction is notneeded, and the heat-treating can be conducted under normal pressure (inan atmospheric pressure). Thus, the treatment can be conducted in asimple manner.

It is preferable that the carbon member be a graphite crucible. The useof a graphite crucible in the treatment makes it possible to suppressthe flow of the gas around the embedded carbon substrate, and to formthe metal carbide layer without color unevenness and more uniformly onthe surface of the carbon substrate. Moreover, the gas produced from thepowder can be kept in the graphite crucible to a certain degree, so theproduced gas can be utilized effectively. It is preferable that a lid beplaced on the graphite crucible, and the lid serves to further suppressthe flow of the gas around the carbon substrate. Examples of the lidinclude one made of graphite, and a sheet made of graphite. In order torelease the gas produced in the container, it is preferable that an airhole be provided in the container or in the lid. When using a sheet madeof graphite, the air hole is not particularly necessary since the sheetmerely covers the container.

When using carbon powder as the carbon member, it is recommended thatthe metal particles containing a transition metal, the pyrolytichydrogen halide generating agent, and the carbon powder be filled in thecontainer, the carbon substrate be embedded in the powder filled in thecontainer, and the carbon substrate be heat-treated. When using carbonpowder as the carbon member, the container is not particularly limited.In the treatment, it is possible to suppress the flow of the gas in thecontainer by, for example, putting a lid or a sheet made of graphite onthe container. It is also possible to use the above-mentioned graphitecrucible as the container.

As described above, an introduced gas is not directly blown into thecontainer in which the carbon substrate is embedded. Conversely, if anattempt is made to carry out the treatment while introducing a hydrogengas, it is difficult to perform the treatment using the hydrogen gasefficiently because the container, such as the graphite crucible,hinders introduction of the hydrogen gas.

Next, one example of the heating apparatus for carrying out the heattreatment in the carbon material manufacturing method of the presentinvention will be described with reference to FIG. 1. The followingdescription is made about a case in which a graphite crucible is used asthe carbon member.

As illustrated in FIG. 1, a heating apparatus used in the carbonmaterial manufacturing method of the present invention (the presentheating apparatus) has a heating furnace 1 having a heater forheat-treating a treatment material placed in the heating furnace 1. Theheating furnace 1 is provided with a gas inlet port 4 and a gas exhaustport 5. An inert gas such as nitrogen gas and argon gas can beintroduced from the gas inlet port 5, as necessary.

In the present heating apparatus, a graphite crucible 6 is disposed inthe heating furnace 1. The graphite crucible 6 is configured so thatpowder 3 (surface modifying agent) can be filled in the graphitecrucible 6, a carbon substrate 2 to be treated can be embedded in thepowder 3, and further, a lid 7 can be placed on the graphite crucible 6.The lid 7 has an air hole. The powder 3 contains a pyrolytic hydrogenhalide generating agent and metal powder (metal particles) containing atransition metal. It is possible to add alumina powder, which is notinvolved in the reaction, to the powder 3.

With the heating apparatus of FIG. 1, the powder 3 is filled in thegraphite crucible 6 as the carbon member, the carbon substrate 2 isembedded in the powder 3 filled in the crucible, and the lid is putthereon. Then, the graphite crucible 6 is placed in the heatingapparatus and heated. With the above-described configuration, the carbonmaterial manufacturing method of the present invention can beimplemented.

A carbon material of the present invention has a metal carbide layercontaining a metal and M₂C or M₃C₂ (M: a transition metal element) on acarbon substrate, and a metal layer on the metal carbide layer. It ispreferable that the M be Cr. It is also preferable that the metalcontained in the metal carbide layer be a transition metal, such as Cr,Fe, and Ni, or an alloy thereof. It is preferable that the maximumthickness of the metal carbide layer be 100 μm or less. On the otherhand, when the minimum thickness of the metal carbide layer exceeds 0μm, the advantageous effects of the present invention can be exhibited.Nevertheless, in order to obtain the advantageous effects moresufficiently, it is desirable that the minimum thickness be 0.5 μm orgreater.

This configuration makes it easy to join the carbon material of thepresent invention with a metal member with the use of a joining materialmade of a metallic material. Accordingly, the joining strength can beimproved. Providing a metal layer on the metal carbide layer in this waymakes it possible to join the carbon material with a metal member.Thereby, it becomes possible to impart the characteristic of a carbonmaterial to a metal material, which cannot be achieved by the metalalone.

The carbon material according to the present invention can bemanufactured by performing the treatment using transition metals showingdifferent reactivity from one another in the carbon materialmanufacturing method of the present invention. It is preferable that thetransition metals contain Cr because the high reactivity of Cr withcarbon can be utilized and the carbon material having a metal carbidelayer containing Cr₂C can be manufactured easily. Moreover, the carbonmaterial having a metal carbide layer containing Cr₂C, Fe, and Ni isespecially preferable, because it can be produced at one time of thetreatment by using powder of, for example, stainless steel containingCr, Fe, and Ni, and a plating layer of Ni or the like can be easilyformed later.

Furthermore, since a plating layer can be formed firmly thereon, thecarbon material can be easily bonded by an adhesive agent to a metalplate such as an aluminum plate, which can be used as a heat radiationplate.

EXAMPLES

Hereinbelow, the present invention will be described in further detailbased on examples thereof. However, the present invention is not limitedthereto.

Examples 1 to 5

Using an apparatus shown in FIG. 1, a mixture powder of stainless steelpowder (SUS 314 powder), ammonium chloride (NH₄Cl), and alumina powder(Al₂O₃) was filled in a graphite crucible (made by Toyo Tanso Co., Ltd,Model number IG-11), and a carbon substrate (high-density isotropicgraphite subjected to cold isotropic pressure forming: bulk density 1.8,average pore radius 5 μm, porosity 20%) having dimensions of 10 mmwide×60 mm long×10 mm thick was embedded in the mixture powder filled inthe crucible. The crucible was placed in the heating furnace with a lidput thereon, and a heat treatment was performed. When heating, nitrogenwas introduced from the gas inlet port, and the gas was dischargednaturally from the gas exhaust port.

Comparative Examples 1 and 2

The carbon substrate was heat-treated in the same manner as described inExample 1, except that the graphite crucible was not used and in placeof the graphite crucible, a porcelain crucible was used as thecontainer.

The treatment conditions for the examples and the comparative exampleswere as set forth in Table 1 below.

TABLE 1 Pressure Treatment inside Powder (wt %) Type of temperatureTreatment time furnace SUS crucible (° C.) (min.) (Torr) powder NH₄ClAl₂O₃ Ex. 1 Graphite 800 30 760 81.2 18.3 0.5 Ex. 2 crucible 1000 30 Ex.3 1200 30 Ex. 4 1000 60 Ex. 5 1000 180 Comp. Porcelain 800 30 Ex. 1crucible Comp. 800 120 Ex. 2

The carbon materials heat-treated and produced according to theseexamples and comparative examples were evaluated for the followingelements. The results of the evaluations are shown in Table 2.

(1) The condition of the layer formed on the carbon substrate(Condition)

The produced carbon materials were evaluated by visual observation andcross-sectional SEM image observation.

(2) Identification of the layer formed on the carbon substrate (Metalcarbide layer)

For each of the produced carbon materials, the layer formed thereon wasidentified by analyzing the metals in vacuum using an EPMA analyzerEMAX-7000 made by Horiba Ltd.

(3) Thickness of the layer formed on the carbon substrate (Thickness)

The produced carbon materials were evaluated by visual observation andcross-sectional SEM image observation.

(4) Adhesion strength between the produced carbon material and the metallayer formed on the carbon material (Adhesion strength)

For each of the produced carbon materials, a 2-μm Ni-plating layer wasformed thereon by electroless plating, and the adhesion strength of theplating layer was determined according to JIS H 8666.

TABLE 2 Metal Thick- Adhesion carbide ness strength Condition layer (μm)(Kgf/cm²) Ex. 1 The layer was formed Cr₂C 1 150 substantially uniformlyover the Fe—Ni entire surface of the carbon alloy substrate. Ex. 2 Thelayer was formed Cr₂C 6 150 substantially uniformly over the Fe—Nientire surface of the carbon alloy substrate. Ex. 3 The layer was formedCr₂C 8 150 substantially uniformly over the Fe—Ni entire surface of thecarbon alloy substrate. Ex. 4 The layer was formed Cr₂C 6 —*¹substantially uniformly over the Fe—Ni entire surface of the carbonalloy substrate. Ex. 5 The layer was formed Cr₂C 8 —*¹ substantiallyuniformly over the Fe—Ni entire surface of the carbon alloy substrate.Comp. The layer could not be formed Cr₂C 1 —*² Ex. 1 over the entiresurface of the Fe—Ni carbon substrate, and color alloy unevennessoccurred. Comp. The layer could not be formed Cr₂C 1 —*² Ex. 1 over theentire surface of the Fe—Ni carbon substrate, and color alloy unevennessoccurred. *¹Adhesion strength was not measured for Examples 4 and 5.*²Adhesion strength was impossible to measure for Comparative Examples 1and 2 because no layer was formed thereon.

As seen from the above results, when no carbon member was used, themetal carbide layer could not be formed over the entire surface of thecarbon substrate, and color unevenness occurred, so the metal carbidelayer could not be formed uniformly on the carbon substrate. Inaddition, it is demonstrated that the carbon materials manufacturedaccording to the carbon material manufacturing method of the presentinvention showed very high adhesion performance with the later-formedmetal layer.

INDUSTRIAL APPLICABILITY

The carbon material manufacturing method according to the presentinvention makes it possible to modify the surface of the carbonsubstrate by a very simple treatment, merely by embedding a carbonsubstrate in powder and heating the substrate.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1 heating furnace    -   2 carbon substrate    -   3 powder    -   4 gas inlet port    -   5 gas exhaust port    -   6 graphite crucible    -   7 lid

The invention claimed is:
 1. A method of manufacturing a carbonmaterial, characterized by heat-treating a carbon substrate togetherwith a carbon member other than the carbon substrate in an inert gasatmosphere without introducing a hydrogen gas which comprises onlyhydrogen, the carbon substrate placed in a surface modifying agentcomprising a pyrolytic hydrogen halide generating agent and metalparticles containing a transition metal, wherein the metal particles areparticles of an alloy containing Cr; and a metal carbide layercontaining a metal and Cr₂C or Cr₃C₂ is formed on a surface of thecarbon substrate.
 2. The method of manufacturing a carbon materialaccording to claim 1, characterized in that: the carbon member comprisesa container made of carbon; and the heat-treating is performed with alid made of graphite or a sheet made of graphite placed on the containerafter placing the carbon substrate, placed in the surface modifyingagent, in the container.
 3. The method of manufacturing a carbonmaterial according to claim 2, characterized in that; the carbon membercomprises carbon powder; and the carbon substrate, placed in the surfacemodifying agent containing the carbon powder, the metal particlescontaining a transition metal, and the pyrolytic hydrogen halidegenerating agent, is heat-treated.
 4. The method of manufacturing acarbon material according to claim 3, characterized in that theheat-treating is performed under normal pressure.
 5. The method ofmanufacturing a carbon material according to claim 3, characterized inthat the pyrolytic hydrogen halide generating agent is ammoniumchloride.
 6. The method of manufacturing a carbon material according toclaim 2, characterized in that the heat-treating is performed undernormal pressure.
 7. The method of manufacturing a carbon materialaccording to claim 2, characterized in that the pyrolytic hydrogenhalide generating agent is ammonium chloride.
 8. The method ofmanufacturing a carbon material according to claim 1, characterized inthat; the carbon member comprises carbon powder; and the carbonsubstrate, placed in the surface modifying agent containing the carbonpowder, the metal particles containing a transition metal, and thepyrolytic hydrogen halide generating agent, is heat-treated.
 9. Themethod of manufacturing a carbon material according to claim 8,characterized in that the heat-treating is performed under normalpressure.
 10. The method of manufacturing a carbon material according toclaim 8, characterized in that the pyrolytic hydrogen halide generatingagent is ammonium chloride.
 11. The method of manufacturing a carbonmaterial according to claim 1, characterized in that the heat-treatingis performed under normal pressure.
 12. The method of manufacturing acarbon material according to claim 1, characterized in that thepyrolytic hydrogen halide generating agent is ammonium chloride.
 13. Amethod of manufacturing a carbon material characterized by heat-treatinga carbon substrate together with a carbon member other than the carbonsubstrate, the carbon substrate placed in a surface modifying agentcomprising a pyrolytic hydrogen halide generating agent and metalparticles containing a transition metal, wherein the carbon substratehas an average pore radius of 5-10 μm, wherein the metal particles areparticles of an alloy containing Cr; and a metal carbide layercontaining a metal and Cr₂C or Cr₃C₂ is formed on a surface of thecarbon substrate.